1. Field of the Invention
The field of this invention lies within the ultrasonic bonding art. It particularly resides within the scope and field wherein wires are bonded to semiconductors. It is known to bond such wires to semiconductors in order to provide leads from semiconductors to certain terminals and other areas.
2. Background of the Invention and Prior Art
Wedge bonding for semiconductors is known in the art as a practical and expedient method to bond wires to semiconductors. Such bonding employs machinery and methods with a wire oftentimes formed of aluminum. The aluminum wire is connected from one point to another by the bonding. The diameter of such wire in many cases can range from between 0.001 to 0.025 inches.
To initiate a bond, the wire is pressed against a semiconductor chip or integrated circuit with a bonding tool. The end of the tool is vibrated with an ultrasonic vibration in a plane of motion generally parallel to the surface of the semiconductor chip to which a wire bond is to be formed. This ultrasonic vibration is for a period of tens of milliseconds.
The combination of a static load on the bonding tool normal to the chip's surface to which the wire is bonded and the vibration at the end of the tool parallel to the surface causes the wire to plastically deform. As the wire plastically deforms, it simultaneously joins with the atoms of the material composing the chip's surface to provide a cold weld.
One of the most difficult problems associated with wire bonding is the manipulation and clamping of the wire and the severing of it after a bond. To perform these functions most fine wire wedge bonders, present and past, have used conventional actuators such as solenoids or voice coils that feed and break the wire, and/or open and close wire clamps.
Such conventional actuators which are driven by solenoids or voice coils have an attendant problem with respect to longevity and their electro-mechanical functions. As can be appreciated, with a solenoid, the moving parts of the solenoid cause friction, and respective interference and wear points. Also, solenoids do not operate as smoothly as other devices.
Another problem with solenoids is that they can not be programmed by a computer. This particular invention has enabled the state of the art of wire bonding to be substantially computerized as to movement and control of the actuation of the movement of the wire and/or the opening and closing of the wire clamps for holding the wire.
The bond head of this invention does not require physical adjustment. It is fundamentally software driven and controlled. The features of the invention are enhanced as to both control and inputs.
In order to effectuate the control, a menu or series of commands can be generated at a keyboard or other input means. This provides not only adjustment, but control of the bond head. The overall adjustment is created in a manner whereby the input to the control means and the mechanical moving means is substantially enhanced. The mechanical movement or drive functions of the invention comprises stepper motors. The control of the stepper motors is with an onboard computer on the bond head.
In the bond head of this invention, 2 miniature stepper motors are used for actuating a wire clamp. One opens and closes the clamp as shown in FIG. 4. The other moves it forwardly or backwardly to feed wire for a first bond and a breaking of the wire after a second bond has been made as shown in FIG. 3. Both stepper motors use cams for smooth motion. The miniature stepper motors in the bond head are computer controlled and require no manual adjustment. The wire clamp opening is taught by the operator using the control panel.
The wire feed and wire break or severance are each programmable. The operator can also increase or decrease the tail length of the first bond by simply changing the number in a wire parameter screen. The same is true for providing a break or severance distance. Each motor has dedicated sensors for providing a home position and direction verification. They are both controlled by a local microcontroller (see FIG. 7). This microcontroller communicates with the main CPU in the bonder via the serial peripheral interface (SPI) provided with the microcontroller chip (see FIG. 6).